* RSV Core Assembly: It’s All About Nucleation Title page * RSV Core Assembly: It’s All About Nucleation Carmen Butan, Giovanni Cardone, Naiqian Cheng, Bernard Heymann, Paul Keller, Dennis Winkler Laboratory of Structural Biology, NIAMS-NIH Parvez Lokhandwala, John Purdy, Rebecca Craven Pennsylvania State University College of Medicine

Retroviruses are highly variable in their capsid architecture, both for a given retrovirus and between different retroviruses.   With HIV, the predominant capsid morphology is biconical; with Rous sarcoma virus, it is irregular polyhedra. Cylindrical tubes with and without end-caps are also produced. .

Butan et al. (2008) J. Mol. Biol., 376, 1168-81 Cryo-electron tomogram of Rous sarcoma virus Butan et al. (2008) J. Mol. Biol., 376, 1168-81

Angular, curved and miscellaneous cores

Virions with angular cores have many spikes: Virions with tubular cores have few spikes

In retroviruses, the capsid assembles de novo inside the provirion, post-budding Not all of the capsid protein assembles: > 50% remains unassembled (Prevelige et al; Fuller et al)

Angular cores correlate with high CA assembly efficiencies: Tubular cores correlate with low CA assembly efficiencies Measure #Gag ( total # CA) from virion diameter

Observations The range of polymorphic variation is very large tubular cores and many “curved”cores - including biconical RSV cores - fail to package RNP Hypothesis: a viable core is one that is closed and has successfully packaged the genome(s) and the polymerase

Observations The range of polymorphic variation is very large tubular cores and many “curved”cores - including biconical RSV cores - fail to package RNP Hypothesis: a viable core is one that is closed and has successfully packaged the genome(s) and the polymerase Inference: Initiation is key to capsid assembly

Critical concentrations for assembly conc’n of protein subunits in capsids Total conc’n of protein subunits

Nucleation of angular nucleocapsid assembly : a model